Neural stimulation has been the subject of a number of studies and has been proposed for several therapies. The autonomic system controls physiological activities of the body and the imbalance of autonomic tone is related to many diseases and conditions. Reduced autonomic balance (increase in sympathetic and decrease in parasympathetic cardiac tone) during heart failure has been shown to be associated with left ventricular dysfunction and increased mortality. Sympathetic inhibition, as well as parasympathetic activation, have been associated with reduced arrhythmia vulnerability following a myocardial infarction. Vagus nerve stimulation has been proposed to treat breathing disorders, gastrointestinal motility, eating disorders, obesity, anorexia, gastrointestinal tract disorders, hypertension, coma, and epilepsy. Direct electrical stimulation of parasympathetic nerves can activate the baroreflex, inducing a reduction of sympathetic nerve activity and reducing blood pressure by decreasing vascular resistance. Direct stimulation of the vagal parasympathetic fibers has been shown to reduce heart rate via the sympathetic nervous system. In addition, some research indicates that chronic stimulation of the vagus nerve may be of protective myocardial benefit following cardiac ischemic insult.
The ability to activate or stimulate single axons or small groups of axons (nerve bundles) within a common nerve trunk without stimulating other portions of the nerve has been referred to as selective activation. Related to selective activation is the ability to selectively sense and record activity from a single or small group of axons. Selective activation and recording are achievable through complex practices such as current steering for stimulating or the use of inter-fascicular electrodes for stimulating or recording. Another, less complex, method of achieving selective activation and recording involves the use of selective geometries. Neural stimulation electrodes presently used for selective activation of peripheral nerves include intraneural wire and silicon array electrodes, epineural electrodes, and multiple contact nerve cuff electrodes. These electrodes can, both in implantation and chronic use, cause mechanical irritation or insult due to the fragility of the neural tissue to be stimulated.